Iis this the best orchestra in the world? No. But the Simón Bólivar Youth Orchestra is classical music's hottest ticket, and with good reason. Its 2007 Prom was one of the most memorable of the last 10 years, and tickets for this London residency sold out 10 months ago. If only concerts by our own National Youth Orchestra, full of equally talented players, attracted half this much buzz. The Bólivars, however, bring their own atmosphere - and that is what really matters here.

Not that the quality is lacking. The stage is as packed as the auditorium. There are around half as many players again on the platform as in a regular symphony orchestra, and while the sheer numbers make Gustavo Dudamel's job of co-ordinating the players with absolute precision even more of a challenge, there are moments when size really does make a difference.

When the low introductory tune of Bartók's Concerto for Orchestra really gets going, it's made menacing by the beef of a dozen basses. And when the violins respond in kind, there is a thrilling visceral fullness to the sound that comes from having 44 or so players to hand.

If the hefty string sound is the most striking thing initially, the second movement of the Bartók throws the spotlight on the wind players, who rattle through their melodies in pairs with dexterity if not with throwaway ease.

Dudamel guides them through, but one feels here at least a two-way process at work; the winds seem to lead as much as be led by him when there are small changes of tempo to be negotiated.

The fifth, final movement is launched at breakneck speed - but here the strings excel, making up for the occasional bit of imprecision earlier by dispatching their scurrying, interweaving lines with unanimous precision, building the whole work up to a jubilant climax.

While the Bartók highlights individual sections and players, Tchaikovsky's Fourth Symphony, impassioned and expansive, is the better showcase for the orchestra as a whole - and for Dudamel's pacing. His approach to the Tchaikovsky is more far-reaching.

All is underpinned at its height by the colossal, floor-shaking buzz of those basses. The Bólivars are very good at playing fast and loud, less adept at playing that is magically quiet - something even more difficult to achieve. Dudamel, however, lets them play to their strengths.

The finale, with the solemn Fate motif on the brass scything through the frenzied strings, and with the full orchestral chords hitting the audience like a jab in the solar plexus, is at once devastating and exhilarating. After the Tchaikovsky there is a blackout, and when the lights go up the players - and Dudamel - have quickly changed into their trademark red, blue and yellow tracksuit tops which have been stashed under their chairs throughout the second half.

The encores mean it's party time: first Ginastera, then another trademark, the mambo from Bernstein's West Side Story, with the players jumping up and dancing as they play, or twirling their instruments in the air as their colleagues take the strain. It is loud, fast and very, very tight.

Would the orchestra be what it is without Dudamel? Perhaps it would be more pertinent to put that question the other way around. What is certain is that there is a symbiosis here between conductor and ensemble that is quite electric.